Concatenated control of alternating-current motors.



- R. D. MERSHON. OONOATENATED CONTROL OF ALTERNATING CURRENT MOTORS. 1111110111011 FILED JUNE 11,1906.

@wwwa-o9 l /Wemhon, 314 uniiou 727 5551A hi@ l'ozneuo UNTTED STATES PATENT oEErcE. A

nALPHQcn. Messiaen, or NE-W Yom, N. Y. p

GONCATENATED CiNTOL 0F ALTERNATING-CU'BBENT ME'JJOBS.

T0 all whom 'it may concern Be it known that I, RALPH-.1). MEnsHoN, a citizen vof the United States, residing at New York, in the county and State of N ew York, have invented certain new and useful Improvements in Concatenated Control .of Alternating-Current Motors, of which the following is a specification, reference being had to the drawing accompanying and forming part of the same.

The common method of varying the speed i of a. direct current motor by means of a be wasted if heostatic control alone were' rheostat or e uivalent devices is to a certain degree waste ul, pn account of the unavoidable losses in therheostat. Where two or more motors arelfemployed, however, it is possible to obtain different-speeds by-amaking Various combinations of the motors in series and in multiple. For example, in traction work, using sa two motors, it is customary to connect tie motors in series for half speed, then in multiplefor full or maximum speed. Between zero speed and half speed, produced 'with the motors in series, and between half and full speed, intermediate variations of speed are obtained by means of a rheostator other suitable device or devices. This method, known as series-multiple control, eifects a large saving of energy, amounting roughly, in the case of two motors, to one half what would employed.

In view of the manifest advantages of the plan just outlined, efforts have been made to utilize the same method inthe case of alternating current induction motors, but it has been found that for successful results the plan `must be modified considerably. With .motors 'of this kind, mere connection of the primary elements of the motors, (the ele ment which receives power and that which delivers power being known as the primary and the secondary respectively), in series `or in multiple will not accomplish the result desired. Instead, itis necessary to connect the primary of one motor tothe lsourcepf o current, its secondary to the primary of the Specication of Letters Patent.4

Application @ed J une 11, 190B.

Patented Sept. 29, 1914;. semi no. 321,094.

ries direct current motors. It is more nearly .equivalent t0 series connection of the armatures of shunt direct current motors, the -ields of which are at all times excited at the line Voltage. V

As is well known, the synchronous, or maximum, speed at which motors in concatenatibn ltend to run is the same as the synchronous speed of a single motor with a number of poles equal to the sum of all the numbers of poles ofthe motors in conecteu nation. Forexample, suppose a car driven by four induction motors, with two motors on or 'geared to one axle and two on or geared to the other axle, the gear ratio being the same in both-cases. Suppose motors A and B, on the) one axle,'to have two and four poles respectively, and motors C and D on the other axle to have eight and sixteen poles respectively. Now if these four motors are connected in concatenation,-that is, with the primary of A connected to the line, the secondary of A to the primary of B, the secondary of B to the primary at C, and so on, with a rheostat in the secondary of Df-fthe combination rof four motors will tend to run at a synchronous.

speed corresponding to 2+4+8+16=30 poles, and by means of the rheosta't we can regulate the speed over the whole range #from zero to the tull speed of the combination, that is, the speed of 30 poles less the .slip. If now motor A be omitted, and motor B connected to the line, the synchronous or full speed of ,the combination will correspond to 4-1-8-1-1/61228 poles, and we can again regulate by means of therheo-Y stat, from a speed approximating s ynchro,

nism for 30 poles to o ne approximatmg synchronism'for 28 poles. Ifnow motor A be replaced and B dropped out, leaving A, C

`-and D in concatenation', the. synchronous speed of the combination will cerespond to 2-l-8-l-16z26 poles, with rheostatic regulation from /28- ...to E36-pole speed. Thus, by various combinations, and by the Ause of each motor fsingly, speeds may be obtained corresponding to v30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, and 2 poles, with rheostatic control for intermediate speeds.

It will be ,observed thatfor all speeds except .the lowest, (that corresponding to 30 poles), one or more of the motors, as many as three at some speeds, ,are idle. It :may be stated generally that vall `the synchronous speeds `of which n given set of motors is Capable above the lowest synchronous speed,

motors from the original number. 'Thus in the example given above, to produce l-pole speed the 2-pole and l-pole motors are cut out; to produce l-pole speed the 2-, 4-, and S-pole machines are dropped; etc. In other words, for all speeds except the lowest a part of the equipment is idle, and for some speeds only one motor can be used. This is a manifest disadvantage, and it is therefore the chief object of my invention to provide a system of concatenated control in which more motors may be kept active in combinations corresponding to various synohronous speeds, or even, it' desired, all may be kept active at all speeds. I secure this desirable capability by providing means for varying the number of polesin one or more of the motors. For example, to obtain say 22-pole speed with the four motors mentioned above it is, by the previous methods,

necessary to drop out the 8-pole mot'cr. But if the l-pole motor could be changed to eight poles the original 8-pole machine could be retained, the sum of the numbers of poles of all four motors then being only twentytwo instead of thirty. To obtain QO-pole speed the 2-pole motorv could then be omitted-or, according to my invention, the

4pole motor could be changed to two poles,l

making the numberof poles 1n all iourl machines twenty instead of twenty-two. To obtain l-pole speed, the 2-, 4:-, and S-pole motors could each be changed to sixteen poles and all four then run in multiple. In this way, by varying the number of poles in one or more motors, as many of them as desred can be kept active at the various speeds, thus utilizing the equipment more economically than 1s posslble with the ordinary method of concatenation. At the same time intermediate speeds at any or all steps may be oitained by rheostatic regulation, as des1re Another objectionable feature of concatenated control as previously ractised is the inductive dropor loss of vo tage in the various motors with the result that the motors after the first in the series do not each get its proper pro ortion of the total voltage .impressed on t e concatenated series. This inductive drop or loss of voltage is similar to that which occurs in a transformer and is due tothe same cause, namely, stray magnetic field. This is at all times a disadvantage, but so far as I am aware it has never been overcome. I propose to secure the desired result by the use of one or more condensers connected with the concatenated series of motors at proper points, as will be `fully explained hereinafter.

VFor a more complete description of the various features of the invention reference may now be had to .the annexed drawing,

in which the figure illustrates diagrammatically a simple and convenient embodiment, employing two motors, the combination being capable of operating at tour synchronous speeds. The figure also shows coudensers connected to the leads from the secondary of the first motor to the primary of the sccond to compensate for the inductive drop in the rst motor.

Referring now to the figure, A and B indicate two Ll-pole motors. By tracing the connections in the diagrammatic controller C it will be seen that the primary I of the first motor is connected, through choke coils or auto-transformers c, with a Q-phase source Gr, for the production of four poles, when the controller is in its first position. The secondary winding S, of the motor A, is also connected for four poles, but in the connections are choke coils or auto-transformers e', tapped at their middle points. .These auto-transformers do not allow current (except their magnetizing current) to allow equal currents to flow from thecnds to the centers and out through the taps, and vice versa. The latter are connected, (through slip rings, not shown), to the centers of auto-transformers or choke coils c2, which cause the current to divide and flow out through the halves of the coils, whence they are led, as will be'seen by tracing the controller connections, to the primary winding P of the second motor `fnd delivered thereto at points to roduce four poles. The secondary winding g of the latter motor is connected for four poles, with auto-transformers or choke coils, tapped at their middle points, in the connections as in the former case. In the second motor the taps from the auto-transformersA are brought out to slip rings (not shown), by which they may be connected with suitable regulating means,

pacity, or any combination -of two or more of these, for example all three,.according to the results desired. It will therefore be seen that in the first position of the controller we have two 4-pole motors in concatenationthat is, the primary of the first is connected to the source of power andv its secondary the second motor, while the secon ary winding S of the latter is connected to a rheostat,-the terms rheostat and rheo- -static being used herein to designate any -of the devices mentioned above or any combination thereof. Consequently the two motors in combination tend to`- run at S-pole synchronous speed, though the actual speed in the firstv position of the controller is lower by'reason of the rheostat R.

In the next position of the controllerit will be seen that the connections are main' tained as in the first,'except that the rheo- R, suchV as resistance, or inductance, or ca' flow through their halves in series, but do winding S is connectedwith the rimary of nais,

statig eut -out and the secondary connectibns of the second motor are simply shortclrcuited. Consequently the speed now rises approximately to synchronism Jfor eight po es.

In the third position of the c ntroller the primary P,l of the irst motor, is connected to the source at points to produce two poles.

. The secondary winding S, however, is connected for tour poles through the choke coils orauto-transformersc, and hence is .noninutual to the primary, that is, inductively independent thereof, and consequently is not affected by the primary when the latter. has only two poles.` This condition of nonmutuality is fully explained in my co-pending application 'Serial No. 319,03@ filed on or about May 28, 1906, now Patent No. 931,136, issued August 17, 1909. The secondary winding S being unaiifected by the -pole primary, an additional seconary winding S2, connected for two poles, is provided, preferably on the same structure or core as the other. The same secondary windingF S might be used instead, by making the necessary changes in its connections, but I prefer generally to use an additional wind- Each may then be permanently arranged for its particular number of poles. In this additional secondaryl 'winding the 2- pole connections are led tothe taps which lead from the choke coils or autotransformer-s to the slip rings, not shown, so that urrents induced bythe primary in the secondary winding S2 will be delivered to the` primary P", ot thesecond motor, at points to reduce four poles, as before. The seconrliiry S ofthe latter motor is again con neet/ed with the rheostat Re We therefore have at the third position of the controller a concatenated combination of a 2-pole and a 4-pole motor, tending to run at 6-pole Synchronous speed, but actually at a lower Speed, by reasonv of the rheostat.

In the fourth position of the controller the rheostat is cut out and the connections of the secondary winding S are 'short-circuited, `Agiving approximately G-pole synchronous speed.

In the fifth position the primary P, of

the second motor, is disconnected from the secondary winding S of the first and is connected to the source G in multiple with the irst motor, which is now restored to t-pole connections, At the same time the connections of the secondary windings and S are short-circuited, `so that the speed of the two motors, no longer in concatenation, will be approximately synchronous for four poles.

At this speed the .f2-pole secondary, S2, of motoi' A is non mutual to the primary` ele-. ment, which has four poles, and is consequently unatl'ected thereby.

In the neXt,`or sixth, position of the controllenboth motors are changed to 2-pole oss ,g

and run multiple. inasmuch as the seconcary winding S', 1n the motor B, 1s con- .fnected orfour pbles it becomes non-mutual to the primary when the number of poles in the latt 'f `is changed to two. The second motor there'tere provided with a Q-.pole

secondary winding S3, with its pole connections led to the taps from the centers of the choke coils or auto-transfor1ners, as in the case of secondary Winding,A S2 in motor. A.. The two secondary y indings or" motor B are also preferably on the same structure or core. in this position of the controller it will be seen that the connections oit the secondary windings S vand S3, in motors Al and B respectively, are short-circuited, so

` that, the motors being in multiple, the speed is approximately synchronous for two poles. Thug with only two motors l am'able to produce tour synchronous speeds-corresponding1 to eight, siX, four and two poles, using both motors at every speed. Two of these speeds, that for eight poles and that for sin poles, are produced by concatenation whereas by the methods employed heretofore only one concatenation speed could be obtained, namely, for eight poles. The system is also under rheostatie control for intermediate speeds. Only two such speeds are provided for in the figure, but it is clear that as many rheostatic speeds can be prof.q vided for as desired.

As mentioned before, the transformer action of motors in concatenation results in more or less inductive loss due to the magnetizing' currents in the successive elements. 1t is highly desirable to overcome this objection as iar as possible, and l have accordingly devised a. plan by which very satisfactory results may be obtained in this respect and a more economical and eil'ectivc operation of the system secured. This plan consists, brieiiy stated, in connecting one or more condensers to the system at one or more points. lf a condenser be connected with the secondary of the .last motor oi the series, the condenser being used alone or, preferably, in combination with resistance` or with inductance, or both, (as described in my copending application Serial No. 257,991), the ill effects of stray field can be overcome at starting and the various motors made to receive substantially their proper proportions of the total impressed voltage, or even a greater voltage than they would receive if the stray ield effects were absent. more eiiiective plan, however, is to use soniecapacity in connection with the secondary of the last motor and also connect lcapacities across the terminals of the see- `ondarles of the other motors, that is, 1n

multiple with the primaries fed thereby.`

Such a .cou-rse produces better results not only because the capacityls distributed approrriinately in correspondence with the distribution ot the reaetance, represented by the stray field effects of the motors, but also because with such connections lall the condensers except thatI connected with the secondary oi the last motor will be effective to a degree, at leastat all speeds, whereas the. condenser connected with the secondary oi' the las#L motor will be practically noneliective at full sieed, its effect being greatest at Zero speed and very insignificant at iull speed'or speeds approximating full speed. Hence it capacity were to be used only in` connection with the secondary of the last motor the desired results would not be obtained at speeds near full speed, or at best the improvement would be but slight. This is due to the fact that w .ereas at Zero speed there is ou each secondary full frequency and a voltage bearing certain proportion to the impressed voltage, at tull speed the frequency and volagge of the secondary of the last motor fall to near zero; while the frequencies of theA sec-v ondaries oit the other motors fall only by amounts dependent upon the places ot the motors in the concatenated series, and never iall to zero. Similarlythe voltages ont the secondaries of all the motors but the last do not fall to aero but are maintained at values dependent upon the places of the motors in the series. It will therefore be seen that the condenscrs connected with the secondaries of the intermediate motors will have impressed upon them higher voltages and higher frequencies at the higher speeds, than would be impressed at the. same speeds upon the condenser connected with the last secondary, and will therefore 'be more effective at' such speeds for producing the results desired. I

The values of the several condensers necessary to produce the desired effects can of course be readily determined, and the ei'fect of stray field in the concatenation can thus be overcome to practically any desired extent. Condensers used for this purpose are shown in the drawing, at D, D. r)They are connected across the leads which extend :from the secondary windings of the first motor, A, to the primary of the next motor, B, that is, across an intermediate circuit oi' the concatenated system.- If more than twomotors are used, other eondensers could beA similarly connected, between eachl motor and theone immediately preceding. This feature is of particular vadvantage in -connection with the herein described scheme of concatenation, but is applicable`.to ad* vantage in the prior methods of concatenation and also in the casel of a single motor whose .speed is varied by a method analogous to concatenation, as described, Jfor example, in my co-pending 'application Serial No. 319,033. y

Electrolytic condensers may be used 'With advantage for the purpose just described, particularly in connection with the last motor of the concatenated series. Such a condenser has in it a high loss; which renders it in. general undesirable for use in the primary element ot the motor, but not in the secondary, since in the latter case the. current due to the loss is effective in producing torque, as fully explained in my co-pending application Serial No. 257,991, before mentioned.`

The operation ot the system can also be improved by maliine` suitable change in the total impressed voltage. when change of voltage is made desirable by change of speed. rThe advantages ot .such .f'oltage changes, and convenient and simple means for eiliectiug the same, are fully explained in my (1e/pending application Serial No. 190,440. The means therein described can readily be applied to the present invention.

The specific embodiment ofthe invention illustrated herein employs two motors, but of course the number is immaterial and as many as desired may be employed. Those illustrated are polypliase, in the present instance two-phase. but it is to be understood that the invention is applicable to single phase apparatus as well. t is to be noted however, that with a single phase motor as the first of the set, that is, the motor which is connected to the Source of current, the sueceeding motors are nevertheless polyphase, since the currents from the secondary windin js of all the motors are necessarily polyphase.

1t is not vnecessary that any of the motors yhave a plurality of secondary windings,

since in each case a single winding can be employed for all the nunibersot poles produced in its primary element, by providing suitable devices, such as for example manually or automatically operated switches, Jfor making the necessary changes in the sec ondary connections when the number of poles in the primary is changed. A plu- 'ality ot primary windings, instead of one, may be used if desired on any motor in which the nunhe'r of poles is varied. In such case. each primary winding may be arranged for a particular number of poles and the motor connections changed from one primary winding to another when the number of poles i-s to be changed, instead of changing" the connections on the same WindinO. The type of windings employed, both primary and. secondary, whether drum, polar, `or of the ring type, as shown, or whether open or closed coil. is also immaterial. Nor is it essential that the condensers used to overcome the stray field effacts be distributed among` all the motors, since goed results may be obtained with the condensers hunched at less points or even at one point, depending; upon the. results de ofthe apparatus, etc.

nreadily mbe made by tb rent motor baring primary and se v first named motor to recel ternating current motorsf'b minces r case, 'or upon condidesign or construction in short, numerous variations or modifications to snit particuL lar conditions or circumstances of use can e skilled engineer, 'from the proper scope o defined zby the appended sirod in the partcula `tions imposed. by the Without departure the invention claims.

`Wl1at l claim is;

l. rThe combination 'o t an alternating; curl condary 'elementseacli adapted to operate with dii ferent numb/ers of poles, an alternating; current motor baring Aa primary element connected. with tile secondary element of the 'Ve current therefrom, and' capacity across the connections between the motors.

2. AThe combination. of a plurality of alaving primary and secondary elements each or' which elements adapted tooperate with diierent nnruberso' vpoles7` means for connecting the `motors in concatenation or in multiple with tti-e' saine or different numbers of coles, as desired, and means for connecting capacity acrosstbe secondary terminals of one or more o tbe motors when in concatenation.

3.' The combination of an alternating' current motor having a primary element and a plurality, of independent secondary Windings, alternating current motor baring a rimary element, means for connecting the primary oi tlisiast named motor with any oit the secondary windings of the first named motor, and means for Varyino" the number, of poles in the primary o tor.

l. Tixecombination of a plurality of alterating current motors each having a pri` mary Winding and a plurality of secondary motor windings, means for connecting the motors m multiple-or in concatenation and Jfor 'varying the number oet poles in the primary 'Wmdmgo one or more of the motors, and

v means for connecting capacity across the secondary 'terminals oi one or more ofthe 5. The combination with a plurality of motorsoit'means for connecting the same i' the nrst named mo-v in concatenation or in multiple with the saine or different numbers of poles, as dcsired, and means connected across the terminals of an intermediate circuit of the system when in concatenation, to neutralize to a desired extent the stray field resulting),` from the concatenated connection.

6. The combination with a plurality of motors, controlling means for connecting' the same in concatenation or in multiple at will with the or different numbers 03": poles, as desired, riieostatic means, including;r resistance and capacity, for varying the speed of the combination and or overcoming. to a desired ententtlie e'liects of stray field, said I rlieostatic means being connected with tho controlling means Twhereby to be connected, across or disconnected from the secondary terminals of one of the motors' in concatenation.

motors in concatenation, of one or more y condensers connected across the connections of any two motors of the concatenated sys tem, as set forth. y, y

8. The combination with a plurality of motors in concatenation, oi' condensers connected across the secondary terminals of a plurality oi the motors, as setfortli.

9. combination with a 'plurality of motors in concatenation, of a plurality of condensers distriouted'over the concatenated system and connected in multiple with the respective secondary circuits.7 as sctiortli. .i

lo. The combination with a plurality of' motorsI of cont-rolling means therefor, to connect the motors in concatenation or in multiple with tlie same or different numbers of poles, means connected across the terminels o1? an intermediate circuit of the system. when in concatenation, to overcome to a `de sircd extent the eiiects of stray field resulting, from tlie concatenated connection, and riieostatie speedfvarying means associated with said controlling ineens and the last motor oi' the series.

` RALPH l). MERS-IGN,

ri. The combination With a plurality otA 

